Add a dev-mode freeform option to recents menu

When the developer option for freeform is enabled, provides
a "Freeform" option in the recents task overlay menu. This
is sort-of an analog to the freeform option in N recents;
however, since recents now is part of home, there's no
straightforward way to have multiple freeforms at a time,
so this really is only useful for developers.

Bug: None
Test: manual - enable freeform in dev settings, then pick
      Freeform from recent task overlay menu.
Change-Id: I5d8e95aaffb8fe43e655f705cacdd51859c95d3b
(cherry picked from commit 9beb6bf2)